Electrical connector

ABSTRACT

A device for electrically connecting a coaxial cable to another electrical component comprises a sleeve for receiving an end of the coaxial cable, the sleeve having a pair of elongate conductive members that extend out of the sleeve from the interior thereof for forming a connection with the electrical component and two quantities of solder for connecting each conductive member to a conductor of the coaxial cable, wherein the sleeve is a unitary sleeve and the conductive members both extend out of the same end of the sleeve, at least one of the elongate conductive members being electrical insulated in order to prevent a short circuit between the conductive members. Also disclosed are a plurality of such devices located on a strip which joins at least one of the conductive members of each device, and a method of manufacturing the devices.

This invention relates to electrical connectors, and in particular toconnectors for forming electrical connections to coaxial cables.

It is often necessary to form a connection between a coaxial cable and aprinted circuit board (PCB) or other electrical component and a numberof devices for forming such connections have been proposed, for exampleas described in U.S. Pat. Nos. 3,743,748 and 4,060,887, the disclosuresof which are incorporated herein by reference. One such device which hasbeen widely employed is that sold by Raychem Corporation under theregistered trademark "PinPak". This device comprises a dimensionallyheat-recoverable sleeve that is formed from a pair of component sleeves,each of which contains a quantity of solder. The sleeves are ofdifferent sizes and one end of the larger sleeve and a bond is formedbetween the sleeves by means of a ring of adhesive. A piece of wire isbent so that each end can be inserted into one of the sleeves (one endinto the small sleeve and one end into the end of the larger sleeve thatcontains the smaller sleeve), and the sleeves are partially recovered togrip the wire. In order to terminate a coaxial cable the cable, aftercutting back the jacket, outer conductor and dielectric by appropriateamounts, is inserted into the sleeve and the sleeve is heat recoveredabout the cable so that the conductors of the cable are each connectedto one end of the wire by means of the solder. Afterwards the centralportion of the wire can be removed by means of snips, so that theremaining parts of the wire act as pins for insertion into a PCB orother device.

Although this type of connector works well in practice it is relativelycomplex and requires a complex manufacturing process: The smaller of thetwo sleeves must be partially recovered about one end of the wire and asolder preform, the larger sleeve must be partially recovered aboutanother solder preform and a ring of adhesive, and finally the largersleeve must be accurately positioned over the end of the smaller sleeveand the free end of the wire and partially recovered thereon.

This invention has, as its object, the provision of a similar coaxialcable connection device that can be produced by means of a less complexprocess. According to one aspect, the invention provides a device forelectrically connecting a coaxial cable to another electrical component,which comprises a sleeve for receiving an end of the coaxial cable, thesleeve having a pair of elongate conductive members that extend out ofthe sleeve from the interior thereof for forming a connection with theelectrical component, which may for example be a printed circuit board,and two quantities of solder for connecting each conductive member to aconductor of the coaxial cable, wherein the sleeve is a unitary sleeveand the conductive members both extend out of the same end of thesleeve, at least one of the elongate conductive members beingelectrically insulated in order to prevent a short circuit between theconductive members. By the expression `unitary sleeve` is meant a sleevehaving a single aperture out of which both elongate conductive membersextend.

The device according to the invention can be manufactured by:

(i) forming a pair of elongate conductive members that are connectedtogether at one end and have one free end;

(ii) providing at least one of the conductive members with electricalinsulation;

(iii) bending the conductive members so that their free end portions arebrought into proximity but are offset from one another, aresubstantially parallel and extend in the same direction; and

(iv) locating a sleeve on the free end portions of the conductivemembers, the sleeve having two quantities of solder for connecting eachconductive member to one conductor of the coaxial cable.

This invention has the advantage that the total number of componentsthat need at some stage to be individually handled is reduced, therebyallowing the possibility of lower manufacturing costs. For example, onlyone sleeve is employed and the relatively difficult requirement oflocating one sleeve within another is removed.

Preferably the sleeve is dimensionally heat-recoverable, that is to saythe article has a dimensional configuration that may be madesubstantially to change when subjected to heat treatment. Usually thesearticles recover, on heating, towards an original shape from which theyhave previously been deformed but the term "heat-recoverable", as usedherein, also includes an article which, on heating, adopts a newconfiguration, even if it has not been previously deformed.

In their most common form, such articles comprise a heat-shrinkablesleeve made from a polymeric material exhibiting the property of elasticor plastic memory as described, for example, in U.S. Pat. Nos.2,027,962; 3,086,242 and 3,597,372. As is made clear in, for example,U.S. Pat. No. 2,027,962, the original dimensionally heat-stable form maybe a transient form in a continuous process in which, for example, anextruded tube is expanded, whilst hot, to a dimensionally heat-unstableform but, in other applications, a preformed dimensionally heat-stablearticle is deformed to a dimensionally heat-unstable form in a separatestate.

In the production of heat-recoverable articles, the polymeric materialmay be cross-linked at any stage in the production of the article thatwill enhance the desired dimensional recoverability. One manner ofproducing a heat-recoverable article comprises shaping the polymericmaterial into the desired heat-stable form, subsequently cross-linkingthe polymeric material, heating the article to a temperature above thecrystalline melting point or, for amorphous materials the softeningpoint, as the case may be, of the polymer, deforming the article andcooling the article whilst in the deformed state so that the deformedstate of the article is retained. In use, since the deformed state ofthe article is heat-unstable, application of heat will cause the articleto assume its original heat-stable shape.

Any material to which the property of dimensional recoverability may beimparted may be used to form the sleeve. Preferred materials includelow, medium or high density polyethylene, ethylene copolymers, eg. withalpha olefins such as 1-butene or 1-hexene, or vinyl acetate, polyamidesor fluoropolymers, eg. polytetrafiuoroethylene, polyvinylidine fluorideor ethylene-tetrafluoroethylene copolymer.

The conductive members will normally be joined together outside thesleeve in order to make the devices more robust when they are beinghandled, the portion of the assembly that joins the two members beingcut out, eg. by means of snips or a pair of pliers, after the cable hasbeen connected, to form a pair of pins. Thus the assembly is normally inthe form of a substantially rectangular loop of wire having two oppositesides (which sides form the pins) that are substantially perpendicularto the axis of the sleeve. Since the sides are separated from oneanother along the axis of the sleeve and both parts of the wire exitfrom the same point of the sleeve, one part of the wire will need to bebent back on itself. On one embodiment, a portion of the wire (at leastone of the conductive members) is bent double where it exits the sleeve,thereby gripping the sleeve between the portions thereof on oppositesides of the bend. If desired, however, alternative means may beemployed for holding the conductive members in place, for example theymay extend in the interior of the sleeve between the sleeve wall and thesolder preform, in which case the sleeve may be partially recovered togrip the conductive members against the solder.

In view of the fact that the parts of the conductive members that arelocated inside the sleeve will be in close proximity, normally touchingone another, and because one of the conductors will need to pass throughthe solder connection formed between the other conductive member and oneof the conductors of the coaxial cable, at least one of the conductorswill need to be electrically insulated along at least part of its lengthwhere appropriate but is retained along a certain portion. Alternativelya length of thin heat-shrinkable tubing may be shrunk onto theconductive member. A further way of insulating the conductive members isby means of a lacquer or enamel.

The devices may be formed individually or they may be provided on astrip so that a bandolier of devices with appropriate inter-devicespacing may be produced and employed with automatic installationequipment or may be employed in multicable connectors, eg. flatconnectors, in which a plurality of coaxial cables are terminated. Insuch a case it is appropriate for the strip to join at least one of theconductive members of each device. For example, and preferably, bothconductive members are attached to the strip, and the strip is cut awayafter the coaxial cables have been terminated in the sleeves.

Thus, according to another aspect, the invention provides a method ofmanufacturing a plurality of devices for electrically connecting acoaxial cable to a printed circuit board, which comprises:

(i) forming a strip of metal from which two sets of elongate conductivemembers extend;

(ii) providing the conductive members of at least one set withelectrical insulation;

(iii) bending the conductive members so that the end portions remotefrom the strip of each conductor of one set are brought into proximitywith the end portions remote from the strip of the correspondingconductor of the other set but are offset from one another, aresubstantially parallel and extend in the same direction; and

(iv) locating a sleeve on the free end portions of each pair ofconductive members, the sleeve having two quantities of solder forconnecting each conductive member to one conductor of the coaxial cable.

The strip and conductive members are preferably formed by stamping themfrom a sheet of metal. After stamping sleeves may be recovered onto eachconductive member of one of the sets and the conductive members may thenbe bent into the required shape, or alternatively each of the legs inone set may be coated with one or more coats of lacquer and optionallyheated to dry and/or cure the lacquer either before or after the bendingstep.

The solder employed in the device is a soft solder as distinct frombrazing material. The solder may, for example, simply be in the form ofan Sn₆₃ Pb₃₇ eutectic composition which will melt as the device isheated and the sleeve recovers, or more than one solder compositionhaving differing melting points may be employed, as described inInternational Application No. WO88/09068. In this form of device,melting of the higher melting point component, eg. Sn₉₆.5 Ag₃.5 eutecticwill provide a visual indication that the device has been heatedsufficiently to melt the lower melting point composition and to form asatisfactory solder joint. If desired the lower melting point solder maybe a non-eutectic composition and, for example as described inInternational Application No. PCT/GB90/00234, the higher and lowermelting point solder compositions may together form a eutecticcomposition. For example, a non-eutectic Sn₆₀ Pb₄₀ lower melting pointcomponent may be employed with a higher melting point component formedfrom pure tin in relative amounts that an Sn₆₃ Pb₃₇ eutectic is formed.The disclosures of these two patent applications are incorporated hereinby reference. An advantage of employing a two component solder, andespecially a tin, Sn₆₀ Pb₄₀ combination is that it reduces thepossibility of "wicking" that is to say, travel of the solder along theconductors and away from the joint area due to capillary action by thestranded conductors, which can be caused by prolonged heating of thedevice.

The heat-recoverable sleeve that is located on the conductive members isnovel per se, and so, according to yet another aspect, the inventionprovides a dimensionally heat-recoverable sleeve for connecting acoaxial cable to a pair of elongate conductive members, the sleeve beingof unitary form and containing two quantities of solder for connectingeach conductive member to one of the conductors of the coaxial cable,and the sleeve having a guide channel to allow insertion of a pair ofelongate conductive members therein so that each conductive member canbe inserted only as far as a different quantity of solder.

The sleeve may be employed for connecting a coaxial cable to a number ofdifferent conductors. For example the sleeve may be positioned on a pairof conductive members as described above. Alternatively it may bepositioned on a pair of pins that extend from a connector, or it can bepositioned on a pair of pre-stripped wires if desired.

Several devices in accordance with the present invention will now bedescribed by way of example, with reference to the accompanyingdrawings, in which:

FIG. 1 is a side sectional elevation of a connector in according to thepresent invention;

FIGS. 2 to 5 show various stages during the manufacture of a deviceaccording to the invention;

FIG. 6 shows a conventional coax-pcb termination device;

FIG. 7 is a sectional elevation showing a second form of deviceaccording to the invention;

FIG. 8 is an end view of the sleeve employed in the device of FIG. 7;and

FIG. 9 is a side view of the sleeve employed in the device of FIG. 7together with a number of alternative conductive members.

Referring to the accompanying drawings, FIG. 1 shows a device 1according to the invention together with an end portion of a coaxialcable 2 inserted therein. The device 1 comprises a sleeve 3 formed fromcrosslinked polyvinylidine fluoride that has been expanded to render itdimensionally heat-recoverable. The sleeve contains a pair of solderrings 4 and 5 that are axially separated and are of different sizes. Inaddition the device includes a wire 6, part of which has been insulatedby means of a heat-shrinkable sleeve recovered thereon. The wire is bentinto a substantially rectangular loop and has two end portions 8 and 9that have been brought together, and extend in the same direction andare substantially parallel. The ends of the wire are offset so that whenthe sleeve is installed on the wire as shown in FIG. 1 the ends 10 and11 of the wire are each located within a different solder ring 4 and 5.The insulating sleeve 7 extends from a region adjacent to the end 11 ofthe wire to an intermediate region of the wire, and insulates the endregion 9 of the wire from the end region 8 of the wire and from anysolder connection between end region 8 of the wire formed by the solderring 4.

As soon as the insulated portion of the wire exits the sleeve it is bentback on itself to form a "U" shaped portion having an arm 12 inside thesleeve 3 and an arm 13 outside the sleeve. This "U" shaped portion willgrip the part of the wall of the sleeve 3 enclosed therein when thesleeve is partially recovered, with the result that the wire and thesleeve are held together. The substantially rectangular loop formed inthe wire has a pair of opposed sides 14 and 15 which extendsubstantially perpendicularly from the axis of the sleeve 3, and anintermediate part 16 of the wire joins the two sides together.

In order to terminate a coaxial cable 2 for connection to a pcb, thejacket 20, braid 21, and dielectric 22 are each cut back so that anappropriate length of the central conductor 23, dielectric and braid areexposed. The end of the coaxial cable is then inserted into the open endof the sleeve 3 as shown in FIG. 1 so that the central conductor 23 andthe braid 21 are in register with the solder rings 4 and 5 respectively.The sleeve is then heated by means of a hot-air gun or an infrared lampin order to cause the sleeve 3 to recover about the coaxial cable 2 andthe solder rings 4 and 5 to fuse and form solder connections between thewire 6 and the conductors of the coaxial cable. Finally the wire 6 iscut at the position of line I--I to remove the intermediate part 16 anda small portion of each opposed side 14 and 15 so that the remainingportions of the wire 6 form a pair of connection pins for connection tothe pcb.

FIGS. 2 to 5 show various stages in the manufacture of a strip ofidentical devices according to the invention. A strip 31 formed fromtinned copper has a set of pins 32 extending from one side thereof and afurther set of slightly longer pins 33 extending from the other sidethereof. The strip is formed by stamping the profile (and theregistration holes 34) from a sheet of copper followed by a conventionaltinning process.

In the next step, lengths of heat-shrinkable tubing 35 are positioned onthe set of longer pins 33 and heated to recover them about the pins, asshown in FIG. 3. The pins are then bent into the configuration shown inFIG. 4 in which a portion of each pin 32 and 33 adjacent to the strip 31extends normally to the plane of the strip, and an end portion 8 and 9of the pins have been brought together and extend parallel to oneanother. In addition, part of the longer pin has a U-shaped bent portion36.

A heat-recoverable polyvinylidine fluoride sleeve 3 partially recoveredabout a pair of solder rings 4 and 5 in order to grip them. This sleeveis then pushed onto one of the pair of bent pins so that part of thewall of the sleeve is gripped by the bent portion 36 of the pin 33. Inthis way a strip of identical devices can be formed. Provision of thestrip 31 facilitates handling of the devices by automated equipment andalso enables a number of coaxial cables to be terminated simultaneously.

By way of comparison, a known coaxial cable termination device is shownin FIG. 6a and b. In order to manufacture the known device a smallheat-recoverable polyvinylidine fluoride sleeve 41 is recovered onto asolder ring 4 and one end of a wire 42. The wire is bent into asubstantially rectangular shape with its other end 43 extending beyondthe end of the sleeve. A second, larger sleeve 44 is partially recoveredonto a solder ring 5 and a ring 46 of uncrosslinked hot-melt adhesive,for example based on polyethylene. The sleeve 44 is then positioned overthe end of the sleeve 41 and the free end 43 of the wire 42 ispositioned inside the sleeve 44 so that it is adjacent to the solderring 5. The assembly is briefly heated so that the sleeve 44 partiallyrecovers about the sleeve 41 and the adhesive ring 46 melts and bondsthe two sleeves together.

FIG. 7 shows another form of device according to the invention which isa slight modification of the device shown in FIG. 1. The device isessentially the same as that shown in FIG. 1 with the exception that theend portions 8 and 9 of the wire 6 extend along the channels in theheat-recoverable sleeve 3 and are located between the solder rings 4 and5 and the sleeve wall. The sleeve may be partially recovered in order togrip the end portions of the wire against the solder. This method ofsecuring the wire 6 in the sleeve 3 obviates the necessity for a "U"shaped part of the wire as shown in FIG. 1.

The sleeve employed in this form of device is shown in FIGS. 8 and 9.The sleeve has a guide channel 40 that receives the end portions of thewire and limit insertion of the wire to the correct extent. The sleevemay, if desired, have a pair of guide channels, one for each conductor,in which case the channels may be of differing bores, the larger bore ofone of the channels being required to accommodate the insulating sleeve7 of the wire 6.

The sleeve shown in FIGS. 8 and 9 may be sold separately from the wire.It may then be employed with a wide range of different conductivemembers of the same general configuration as that of the end portions ofthe wire 6. For example it may be recovered onto pins on a strip in themanner of FIGS. 2 to 5 or it may be recovered onto connector pins 42 oreven pre stripped wires 43.

We claim:
 1. A device arranged to electrically connect a coaxial cableto an electrical component,said device comprising a sleeve arranged toreceive an end of the coaxial cable, the sleeve having an interiorand:(a) a pair of elongate conductive members that extend out of thesleeve from the interior thereof, and being arranged to form aconnection with said electrical component; and (b) two quantities ofsolder arranged to connect each said conductive member to a conductor ofsaid coaxial cable; wherein said sleeve is a unitary sleeve and saidconductive members both extend out of a first end of the sleeve; andwherein at least one of said elongate conductive member is electricallyinsulated in order, in use, to prevent a short circuit between saidconductive members.
 2. A device as claimed in claim 1, wherein thesleeve is dimensionally heat-recoverable.
 3. A device a claimed in claim1 wherein a portion of at least one of said conductive members is bentdouble where it exits said sleeve, thereby gripping said sleeve.
 4. Adevice as claimed in claim 1 wherein said sleeve has been partiallyrecovered thereby to grip the elongate conductive members against thesolder.
 5. A device as claimed in claim 1, wherein said conductivemembers are joined together outside said sleeve.
 6. A plurality ofdevices as claimed in claim 1, said devices being located on a stripwhich joins at least one of said conductive members of each device.
 7. Adimensionally heat-recoverable sleeve arranged to connect a coaxialcable having two electrical conductors to a pair of elongate conductivemembers, said sleeve being of unitary form and containing two quantitiesof solder arranged to connect each conductive members to a respectivesaid one of said conductors of said coaxial cable, and said sleevehaving a guide channel to allow insertion of a pair of elongateconductive members therein so that each said conductive member can beinserted only as far as a different quantity of solder.